The purpose of the project is to study the organization of genes in large DNA molecules obtained from animal viruses. The production and ordering of unique segments of vaccinia virus DNA provide a physical map of the genome. Physical maps have been determined for several different restriction enzymes including SalI, HindIII, XhoI, KpnI, SmaI, and BglI. The last two enzymes are very useful since they cleave the DNA into five easily separated segments from which other restriction enzyme maps can be determined. Viral DNA segments are being cloned in plasmids with the aim of doing sequence determination on the region containing the origin of replication and any possible signal elements in the viral genome. DNA from phage N3 which exists as a prophage in Hemophilus influenzae was characterized. This aggregation of this DNA is caused by single strand tails at the termini. DNA from phage 42, which can lysogenize streptococci, was also studied and shown to be circularly permuted. A new method was developed for examining the extent of this circular permutation.